Update: I was unfortunately not aware of Shamus Young's severe criticism of Fallout 3 available here to link in the original piece and I regret that. It dovetails rather nicely with what I've written and it's much better executed than my piece. I strongly recommend anyone...

When there's no more room in hell, the dead will walk over our garden.

Forget everything you learned with the Romero or Argento zombie flicks of the '70s and '80s. Zombies may be here to roam the Earth and consume our brains as an unstoppable, shambling mob of undead, and they are hungry. However, something stands in their way, their formidable enemy: plants. When there's no more room in hell, so goes the proverb, the dead will come to walk over our pretty little patch of heaven so they can reach us in Plants vs. Zombies.

Plants vs. Zombies from PopCap Games is based on an incredibly simple concept: Don't let the slowly moving zombies get across your lawn by placing defenses in their way, in a simplified tower defense structure. Instead of having maps filled with twists and turns common to games in the genre, you are given a square patch of grass with a limited space for deploying plants. The various types of photosynthesis users can be used offensively or defensively against the incoming horde, starting off with a weak pea shooter that quickly evolves into more interesting upgrades, like cherry bombs.

As you complete each level of zombie defense, you'll unlock new seeds which supply you with more varieties of plants to carry into battle, though there is a limited supply of seeds you can use in a mission. Planting, however, isn't as simple as digging a hole, as each kind of vegetation (sheesh, running out of synonyms here) needs a particular amount of sun power to be grown. This resource is slowly supplied automatically by the sun itself - if the level is occurring during the day - and from sunflowers, if you happen to plant them (which you should). The day and night cycle in the game not only changes how you collect power to build defenses, but also how they act upon attackers, their power, and what attackers show up to threaten your tidy suburban lawn.

Now, the hook in playing Plants vs. Zombies lies in how the levels work. As you progress, your defenses grow and the zombie waves become thicker and thicker, until by the end of the mission, the game decides to take off the kid gloves and unleashes a giant horde at you. While the normal progression is generally easy-going, the horde can be a slap to the face if you leave holes in your plan. This makes for a deceptive feeling of security before a raging storm, which is rarely associated with tower defense games, which normally boil down to pure math in most other titles. Not in Plants vs. Zombies. At points, you'll swear you are playing Left 4 Dead in a shifted, cartoony perspective for short spans of time, especially when the zombies start to come in a variety of shapes and sizes, each with their own approach to attacking you.

Not everything is an all-out war against the rotting kind. Thrown in between the normal tower defense levels are special, more laid-back arcade stages, like a bowling alley, that work as both an introduction to a new tool and a rest station for the weary zombie fighter. These don't change the overall objective of impeding the zombie movement, but they do change the means to do it quite a bit.

This variety and sense of not knowing what's next is what keeps Plants vs. Zombies fresh - as fresh as rotting zombies can be - and fun. There are also other game modes that become available once the main story mode has been completed, modes that pit you against increasingly overwhelming odds against the undead survival-style. In the two puzzle modes, you get a chance to play as the undead for a change of pace, deploying your units as a zombie overlord - count me as a traitor, but I love playing as the opposition in this case. The other puzzle mode titled Vasebreaker, plays more like an odds game - various vases litter your garden, some containing lovely prizes, but also zombies.

It's probably a first, but the zombies in this game are actually cute. No, I'm not saying you'll see zombie poodles or parrots anytime soon, but the art style really gets it right, pitting happy-go-lucky plants against the undead in a way that doesn't seem too implausible. Come on, this is a game, we can have these two impossible scenarios mix up - the dead coming back alive and plants defending our homes - can't we? The zombies have their characteristic moans and various catch-phrases and humorous lines, and the music helps the action along as it shifts depending on how successful you are at any given moment.

Plants vs. Zombies might seem like a dumbed-down tower defense game at first, but like Swords and Soldiers proved, depth can be found in simple games. Regardless of which side you pick to defend, you'll find an interesting and highly enjoyable game in Plants vs. Zombies, no matter how long you have to play.